Comparison of domestic hot water production with photovoltaic panels and solar thermal collectors

A photovoltaic (PV) heated domestic hot water system with direct electrical heating is investigated experimentally in 2024 under Danish weather conditions. The tank has five electrical heating foils on the outer vertical surface. The foils are supplied with electricity from PV panels or the grid. A semi-smart controller allows the tank to be heated with grid electricity at night to establish the energy needed the following day. The measured data are analysed, and the numerical model is validated against them. The model is subsequently used for annual performance simulations. The PV system is compared to a similar solar domestic hot water (SDHW) system with electrical backup heating, and the performance, cost, CO2 emissions, and levelized cost of heat (LCoH) are determined. The performances and CO2 emission reduction of the two systems are similar, despite the PV system having an area three times that of the SDHW system. The PV system costs approximately twice as much as the SDHW system, while CO2 emissions from production, installation, and end-of-life are 3.75 times higher. LCoH for the PV system (0.34 €/kWh) is approximately 1.5 times higher than LCoH for the SDHW system (0.23 €/kWh). Consequently, only the SDHW system is currently economically attractive.